The Experts below are selected from a list of 141369 Experts worldwide ranked by ideXlab platform
Dean R. Hess - One of the best experts on this subject based on the ideXlab platform.
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Continuous positive airway pressure in new-generation mechanical ventilators: a Lung Model study.
Anesthesiology, 2002Co-Authors: Muneyuki Takeuchi, Dean R. Hess, Purris Williams, Robert M. KacmarekAbstract:BACKGROUND A number of new microprocessor-controlled mechanical ventilators have become available over the last few years. However, the ability of these ventilators to provide continuous positive airway pressure without imposing or performing work has never been evaluated. METHODS In a spontaneously breathing Lung Model, the authors evaluated the Bear 1000, Drager Evita 4, Hamilton Galileo, Nellcor-Puritan-Bennett 740 and 840, Siemens Servo 300A, and Bird Products Tbird AVS at 10 cm H(2)O continuous positive airway pressure. Lung Model compliance was 50 ml/cm H(2)O with a resistance of 8.2 cm H(2)O x l(-1) x s(-1), and inspiratory time was set at 1.0 s with peak inspiratory flows of 40, 60, and 80 l/min. In ventilators with both pressure and flow triggering, the response of each was evaluated. RESULTS With all ventilators, peak inspiratory flow, Lung Model tidal volume, and range of pressure change (below baseline to above baseline) increased as peak flow increased. Inspiratory trigger delay time, inspiratory cycle delay time, expiratory pressure time product, and total area of pressure change were not affected by peak flow, whereas pressure change to trigger inspiration, inspiratory pressure time product, and trigger pressure time product were affected by peak flow on some ventilators. There were significant differences among ventilators on all variables evaluated, but there was little difference between pressure and flow triggering in most variables on individual ventilators except for pressure to trigger. Pressure to trigger was 3.74 +/- 1.89 cm H(2)O (mean +/- SD) in flow triggering and 4.48 +/- 1.67 cm H(2)O in pressure triggering (P < 0.01) across all ventilators. CONCLUSIONS Most ventilators evaluated only imposed a small effort to trigger, but most also provided low-level pressure support and imposed an expiratory workload. Pressure triggering during continuous positive airway pressure does require a slightly greater pressure than flow triggering.
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Expiratory phase and volume-adjusted tracheal gas insufflation: a Lung Model study.
Critical care medicine, 1998Co-Authors: Hideaki Imanaka, Robert M. Kacmarek, Ray Ritz, Vincent Riggi, Dean R. HessAbstract:Objective: To evaluate In a Lung Model the effects of expiratory-phase tracheal gas Insufflation (expiratory-phase TGI) with both volume and pressure control ventilation, and tidal volume-adjusted continuous flow TGI (volume-adjusted TGI) on system pressures and volumes. Design: Single-compartment Lung Model. Setting: Research laboratory in a university medical center. Interventions: Expiratory-phase TGI was established, using a solenoid valve activated by the ventilator. Volume-adjusted TGI was applied by reducing tidal volume (VT) by the product of TGI flow and inspiratory time. Ventilation was provided with pressure control of 20 cm H 2 O or volume control ventilation with VT similar to that with pressure control ventilation. A rate of 15 breathslmin and positive end-expiratory pressure (PEEP) of 10 cm H 2 O were used throughout. Inspiratory time periods of 1.0, 1.5, 2.0, and 2.5 secs were used with TGI flows of 0, 4, 8, and 12 L/min. Lung Model compliance (mL/cm H 2 O) and resistance (cm H 2 O/L/sec) combinations of 20/20, 20/5 and 50/20 were used. Measurements and Main Results: In expiratory-phase TGI with pressure control ventilation, peak alveolar pressure remained constant, PEEP increased (p
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Tracheal gas insufflation-pressure control versus volume control ventilation. A Lung Model study.
American journal of respiratory and critical care medicine, 1996Co-Authors: Hideaki Imanaka, Robert M. Kacmarek, Ray Ritz, Dean R. HessAbstract:Tracheal gas insufflation (TGI) has been recommended as an adjunct to mechanical ventilation in the presence of elevated Pa CO2. Based on our initial clinical experience with continuous flow TGI and pressure control ventilation (PCV), we were concerned about elevation in peak airway pressure as TGI was applied. In a Lung Model, we evaluated the effects of continuous flow TGI during both PCV and volume control ventilation (VCV). A single compartment Lung Model was configured with an artificial trachea into which an 8-mm endotracheal tube was positioned. TGI was established with a 16-G catheter positioned 2 cm beyond the tip of the endotracheal tube. Ventilation was provided by a Puritan-Bennett 7200ae ventilator with PCV 20 cm H2O or VCV with a tidal volume (VTt) similar to that with PCV. A rate of 15 breaths/min and PEEP of 10 cm H2O were used throughout. Inspiratory times (TI) of 1.0, 1.5, 2.0, and 2.5 s were used with TGI of 0, 4, 8, and 12 L/min. Lung Model compliance (ml/cm H2O) and resistance (cm H2O...
Indrin J. Chetty - One of the best experts on this subject based on the ideXlab platform.
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SU‐GG‐T‐512: CT Resolution for Lung Treatment Planning: An Application of a 2 ½‐D Random Lung Model Using MC Method
Medical Physics, 2008Co-Authors: L Liang, Edward W. Larsen, Indrin J. Chetty, Muthana Al-ghaziAbstract:Purpose: To investigate the effects of CT resolution on treatment planning where heterogeneities exist, such as in the Lung, using a recently developed, realistic random Lung Model and Monte Carlo method.Method and Materials: A thoracic phantom with a realistic random Lung Model embedded was built and two representative realizations with two different sizes of tumors were generated. The MC code DPM was employed to calculate dose distributions in the phantom with different CT resolutions. The three‐field conformal setup used a 6MV photon beam. Both qualitative and quantitative dose evaluation metrics were applied. Results: A reference CT resolution of 1×1 cm2 was established by comparing the CAX depth doses between a detailed Lung Model and its voxelized version. The fine details revealed in high resolution can be smoothed, especially when the geometrical voxels cross the heterogeneities, hence introducing a potential systematic error. Visible difference, up to 1%, can be seen in the DVHs of the cases with a small tumor. The insensitive relative absolute differential dose shows the DVH's disadvantage of lack of positional information of the dose distribution. Conclusion: A realistic random Lung Model was applied to show the effect of the accuracy of the geometrical representation on dose distribution in heterogonous sites, such as the Lung. Our results show that a CT resolution up to 2×2 mm2 may be sufficient while a 4×4 mm2 could lead to significant perturbations. This may be especially problematic for treatment planning involving small tumors and tissue heterogeneities.
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An anatomically realistic Lung Model for Monte Carlo-based dose calculations.
Medical physics, 2007Co-Authors: Liang Liang, Edward W. Larsen, Indrin J. ChettyAbstract:Treatment planning for disease sites with large variations of electron density in neighboring tissues requires an accurate description of the geometry. This self-evident statement is especially true for the Lung, a highly complex organ having structures with a wide range of sizes that range from about 10 − 4 to 1 cm . In treatment planning, the Lung is commonly Modeled by a voxelized geometry obtained using computed tomography(CT) data at various resolutions. The simplest such Model, which is often used for QA and validation work, is the atomic mix or mean density Model, in which the entire Lung is homogenized and given a mean (volume-averaged) density. The purpose of this paper is (i) to describe a new heterogeneous random Lung Model, which is based on morphological data of the human Lung, and (ii) use this Model to assess the differences in dose calculations between an actual Lung (as represented by our Model) and a mean density (homogenized) Lung. Eventually, we plan to use the random Lung Model to assess the accuracy of CT-based treatment plans of the Lung. For this paper, we have used Monte Carlo methods to make accurate comparisons between dose calculations for the random Lung Model and the mean density Model. For four realizations of the random Lung Model, we used a single photon beam, with two different energies (6 and 18 MV ) and four field sizes ( 1 × 1 , 5 × 5 , 10 × 10 , and 20 × 20 cm 2 ). We found a maximum difference of 34% of D max with the 1 × 1 , 18 MV beam along the central axis (CAX). A “shadow” region distal to the Lung, with dose reduction up to 7% of D max , exists for the same realization. The dose perturbations decrease for larger field sizes, but the magnitude of the differences in the shadow region is nearly independent of the field size. We also observe that, compared to the mean density Model, the random structures inside the heterogeneous Lung can alter the shape of the isodose lines, leading to a broadening or shrinking of the penumbra region. For small field sizes, the mean Lungdoses significantly depend on the structures’ relative locations to the beam. In addition to these comparisons between the random Lung and mean density Models, we also provide a preliminary comparison between dose calculations for the random Lung Model and a voxelized version of this Model at 0.4 × 0.4 × 0.4 cm 3 resolution. Overall, this study is relevant to treatment planning for Lung tumors, especially in situations where small field sizes are used. Our results show that for such situations, the mean density Model of the Lung is inadequate, and a more accurate CT Model of the Lung is required. Future work with our Model will involve patient motion, setup errors, and recommendations for the resolution of CT Models.
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TH‐D‐ValA‐03: An Improved Lung Model, Incorporating Realistic Random Anatomical Features, for Monte Carlo‐Based Dosimetry
Medical Physics, 2006Co-Authors: Liang Liang, Edward W. Larsen, Indrin J. ChettyAbstract:Purpose: To investigate the effects of incorporating a more physically‐realistic Lung Model, preserving random anatomical features of the Lung, on MC‐based dose distributions. Methods: A random Lung Model was built based on morphological data. The Model homogenizes the Lung parenchyma with structures of “chunk” sizes less than 0.05 cm, and Models all larger chunks (branches of the bronchial and vessel trees, up to ∼1.5 cm) as randomly‐positioned 2‐D cylinders. The MC code PENELOPE was employed to calculate dose distributions in a water phantom containing a Lung region, Modeled by either a homogenized Lung (as used in conventional planning) or the random Lung Model. Dose calculations used 6 and 18 MV photon beams with four different field sizes.Results: Depth dose curves in the random Lung Model illustrate significant perturbations when the structure size is comparable to the field size. For the 1×1 cm field size, large differences (up to 34% of Dmax) exist in the largest structures due to the loss of CPE with small field size. For large field sizes (10×10 cm or higher), little difference is observed between the random and the homogeneous Models. The additional attenuation of the large structures also results in a region of dose reduction behind the Lung.Conclusion: A new random Lung Model reveals significant dose perturbations from the homogeneous Model, and shows that the homogeneous Model breaks down when the field size is comparable to the structure size. This work is of importance in IMRT planning, where beamlets are used, or in the treatment of small tumors, where small field sizes are used in the planning. This work suggests that in such cases, a more precise description of the Lung geometry, e.g. a high resolution CT‐based pixel‐by‐pixel density map, may be necessary for accurate dosimetry.
Gerhard Jorch - One of the best experts on this subject based on the ideXlab platform.
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278 MEASUREMENT OF FUNCTIONAL RESIDUAL CAPACITY (FRC) WITH HELIUM/OXYGEN (HELIOX) AS A WASHOUT GAS IN A MECHANICAL Lung Model
Pediatric Research, 1994Co-Authors: Roland Hentschel, Andreas Volbracht, Andreas Suska, Gerhard JorchAbstract:278 MEASUREMENT OF FUNCTIONAL RESIDUAL CAPACITY (FRC) WITH HELIUM/OXYGEN (HELIOX) AS A WASHOUT GAS IN A MECHANICAL Lung Model
Robert M. Kacmarek - One of the best experts on this subject based on the ideXlab platform.
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measured cpap in a noninvasive pediatric airway and Lung Model
Respiratory Care, 2021Co-Authors: Neil D Fernandes, Esther H Chung, Michael D Salt, Beverly Ejiofor, Ryan W Carroll, Robert M. KacmarekAbstract:Background: Bronchiolitis is the most common cause of admission in children under 2 years of age in the United States. The standard of care involves supportive measures, including non-invasive interventions such as CPAP. CPAP is traditionally delivered through a full facemask; however, pediatric intensive care units have been exploring the use of the RAM cannula by Neotech as a mode of CPAP delivery, but the level of CPAP delivered is uncertain. We, therefore, completed an in vitro study to determine the level of CPAP delivered via the RAM cannula utilizing a pediatric Lung Model. Methods: 3D-printed Models of seven sizes of pediatric upper airways were connected to an ASL 5000 Breathing Simulator. We applied each size of RAM cannula to weight-appropriate airway and Lung compliance parameters, delivering pressures of 5, 7 and 10 cmH2O using a ventilator in the CPAP mode. Leaks of 0%, 20%, 40% and 60% were generated to emulate a complete seal or poor fit and/or open-mouth breathing. The outcome measure was the difference in CPAP, referred to as ‘%leak effect’, measured by the Lung simulator relative to the CPAP set on the ventilator. Results: We found that set CPAP of 5 through 10 cmH2O generated measured CPAP ranging from 2.6 to 9.7 cmH2O. For set CPAP of 5, 7 and 10 cmH2O the mean ‘%leak effect’ of measured CPAP from the set CPAP was: -25%, -26% and -25.7%, respectively. For each specific cannula-airway combination, increasing the set pressure and decreasing the air leak resulted in higher levels of CPAP delivered. Conclusion: RAM cannula delivers varying amounts of CPAP, with a percent loss of approximately -25% depending on the level of leak in the system. With minimal leak, it is conceivable that the RAM cannula can be used to deliver clinically meaningful CPAP.
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Continuous positive airway pressure in new-generation mechanical ventilators: a Lung Model study.
Anesthesiology, 2002Co-Authors: Muneyuki Takeuchi, Dean R. Hess, Purris Williams, Robert M. KacmarekAbstract:BACKGROUND A number of new microprocessor-controlled mechanical ventilators have become available over the last few years. However, the ability of these ventilators to provide continuous positive airway pressure without imposing or performing work has never been evaluated. METHODS In a spontaneously breathing Lung Model, the authors evaluated the Bear 1000, Drager Evita 4, Hamilton Galileo, Nellcor-Puritan-Bennett 740 and 840, Siemens Servo 300A, and Bird Products Tbird AVS at 10 cm H(2)O continuous positive airway pressure. Lung Model compliance was 50 ml/cm H(2)O with a resistance of 8.2 cm H(2)O x l(-1) x s(-1), and inspiratory time was set at 1.0 s with peak inspiratory flows of 40, 60, and 80 l/min. In ventilators with both pressure and flow triggering, the response of each was evaluated. RESULTS With all ventilators, peak inspiratory flow, Lung Model tidal volume, and range of pressure change (below baseline to above baseline) increased as peak flow increased. Inspiratory trigger delay time, inspiratory cycle delay time, expiratory pressure time product, and total area of pressure change were not affected by peak flow, whereas pressure change to trigger inspiration, inspiratory pressure time product, and trigger pressure time product were affected by peak flow on some ventilators. There were significant differences among ventilators on all variables evaluated, but there was little difference between pressure and flow triggering in most variables on individual ventilators except for pressure to trigger. Pressure to trigger was 3.74 +/- 1.89 cm H(2)O (mean +/- SD) in flow triggering and 4.48 +/- 1.67 cm H(2)O in pressure triggering (P < 0.01) across all ventilators. CONCLUSIONS Most ventilators evaluated only imposed a small effort to trigger, but most also provided low-level pressure support and imposed an expiratory workload. Pressure triggering during continuous positive airway pressure does require a slightly greater pressure than flow triggering.
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Expiratory phase and volume-adjusted tracheal gas insufflation: a Lung Model study.
Critical care medicine, 1998Co-Authors: Hideaki Imanaka, Robert M. Kacmarek, Ray Ritz, Vincent Riggi, Dean R. HessAbstract:Objective: To evaluate In a Lung Model the effects of expiratory-phase tracheal gas Insufflation (expiratory-phase TGI) with both volume and pressure control ventilation, and tidal volume-adjusted continuous flow TGI (volume-adjusted TGI) on system pressures and volumes. Design: Single-compartment Lung Model. Setting: Research laboratory in a university medical center. Interventions: Expiratory-phase TGI was established, using a solenoid valve activated by the ventilator. Volume-adjusted TGI was applied by reducing tidal volume (VT) by the product of TGI flow and inspiratory time. Ventilation was provided with pressure control of 20 cm H 2 O or volume control ventilation with VT similar to that with pressure control ventilation. A rate of 15 breathslmin and positive end-expiratory pressure (PEEP) of 10 cm H 2 O were used throughout. Inspiratory time periods of 1.0, 1.5, 2.0, and 2.5 secs were used with TGI flows of 0, 4, 8, and 12 L/min. Lung Model compliance (mL/cm H 2 O) and resistance (cm H 2 O/L/sec) combinations of 20/20, 20/5 and 50/20 were used. Measurements and Main Results: In expiratory-phase TGI with pressure control ventilation, peak alveolar pressure remained constant, PEEP increased (p
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Tracheal gas insufflation-pressure control versus volume control ventilation. A Lung Model study.
American journal of respiratory and critical care medicine, 1996Co-Authors: Hideaki Imanaka, Robert M. Kacmarek, Ray Ritz, Dean R. HessAbstract:Tracheal gas insufflation (TGI) has been recommended as an adjunct to mechanical ventilation in the presence of elevated Pa CO2. Based on our initial clinical experience with continuous flow TGI and pressure control ventilation (PCV), we were concerned about elevation in peak airway pressure as TGI was applied. In a Lung Model, we evaluated the effects of continuous flow TGI during both PCV and volume control ventilation (VCV). A single compartment Lung Model was configured with an artificial trachea into which an 8-mm endotracheal tube was positioned. TGI was established with a 16-G catheter positioned 2 cm beyond the tip of the endotracheal tube. Ventilation was provided by a Puritan-Bennett 7200ae ventilator with PCV 20 cm H2O or VCV with a tidal volume (VTt) similar to that with PCV. A rate of 15 breaths/min and PEEP of 10 cm H2O were used throughout. Inspiratory times (TI) of 1.0, 1.5, 2.0, and 2.5 s were used with TGI of 0, 4, 8, and 12 L/min. Lung Model compliance (ml/cm H2O) and resistance (cm H2O...
Edward W. Larsen - One of the best experts on this subject based on the ideXlab platform.
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SU‐GG‐T‐512: CT Resolution for Lung Treatment Planning: An Application of a 2 ½‐D Random Lung Model Using MC Method
Medical Physics, 2008Co-Authors: L Liang, Edward W. Larsen, Indrin J. Chetty, Muthana Al-ghaziAbstract:Purpose: To investigate the effects of CT resolution on treatment planning where heterogeneities exist, such as in the Lung, using a recently developed, realistic random Lung Model and Monte Carlo method.Method and Materials: A thoracic phantom with a realistic random Lung Model embedded was built and two representative realizations with two different sizes of tumors were generated. The MC code DPM was employed to calculate dose distributions in the phantom with different CT resolutions. The three‐field conformal setup used a 6MV photon beam. Both qualitative and quantitative dose evaluation metrics were applied. Results: A reference CT resolution of 1×1 cm2 was established by comparing the CAX depth doses between a detailed Lung Model and its voxelized version. The fine details revealed in high resolution can be smoothed, especially when the geometrical voxels cross the heterogeneities, hence introducing a potential systematic error. Visible difference, up to 1%, can be seen in the DVHs of the cases with a small tumor. The insensitive relative absolute differential dose shows the DVH's disadvantage of lack of positional information of the dose distribution. Conclusion: A realistic random Lung Model was applied to show the effect of the accuracy of the geometrical representation on dose distribution in heterogonous sites, such as the Lung. Our results show that a CT resolution up to 2×2 mm2 may be sufficient while a 4×4 mm2 could lead to significant perturbations. This may be especially problematic for treatment planning involving small tumors and tissue heterogeneities.
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An anatomically realistic Lung Model for Monte Carlo-based dose calculations.
Medical physics, 2007Co-Authors: Liang Liang, Edward W. Larsen, Indrin J. ChettyAbstract:Treatment planning for disease sites with large variations of electron density in neighboring tissues requires an accurate description of the geometry. This self-evident statement is especially true for the Lung, a highly complex organ having structures with a wide range of sizes that range from about 10 − 4 to 1 cm . In treatment planning, the Lung is commonly Modeled by a voxelized geometry obtained using computed tomography(CT) data at various resolutions. The simplest such Model, which is often used for QA and validation work, is the atomic mix or mean density Model, in which the entire Lung is homogenized and given a mean (volume-averaged) density. The purpose of this paper is (i) to describe a new heterogeneous random Lung Model, which is based on morphological data of the human Lung, and (ii) use this Model to assess the differences in dose calculations between an actual Lung (as represented by our Model) and a mean density (homogenized) Lung. Eventually, we plan to use the random Lung Model to assess the accuracy of CT-based treatment plans of the Lung. For this paper, we have used Monte Carlo methods to make accurate comparisons between dose calculations for the random Lung Model and the mean density Model. For four realizations of the random Lung Model, we used a single photon beam, with two different energies (6 and 18 MV ) and four field sizes ( 1 × 1 , 5 × 5 , 10 × 10 , and 20 × 20 cm 2 ). We found a maximum difference of 34% of D max with the 1 × 1 , 18 MV beam along the central axis (CAX). A “shadow” region distal to the Lung, with dose reduction up to 7% of D max , exists for the same realization. The dose perturbations decrease for larger field sizes, but the magnitude of the differences in the shadow region is nearly independent of the field size. We also observe that, compared to the mean density Model, the random structures inside the heterogeneous Lung can alter the shape of the isodose lines, leading to a broadening or shrinking of the penumbra region. For small field sizes, the mean Lungdoses significantly depend on the structures’ relative locations to the beam. In addition to these comparisons between the random Lung and mean density Models, we also provide a preliminary comparison between dose calculations for the random Lung Model and a voxelized version of this Model at 0.4 × 0.4 × 0.4 cm 3 resolution. Overall, this study is relevant to treatment planning for Lung tumors, especially in situations where small field sizes are used. Our results show that for such situations, the mean density Model of the Lung is inadequate, and a more accurate CT Model of the Lung is required. Future work with our Model will involve patient motion, setup errors, and recommendations for the resolution of CT Models.
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TH‐D‐ValA‐03: An Improved Lung Model, Incorporating Realistic Random Anatomical Features, for Monte Carlo‐Based Dosimetry
Medical Physics, 2006Co-Authors: Liang Liang, Edward W. Larsen, Indrin J. ChettyAbstract:Purpose: To investigate the effects of incorporating a more physically‐realistic Lung Model, preserving random anatomical features of the Lung, on MC‐based dose distributions. Methods: A random Lung Model was built based on morphological data. The Model homogenizes the Lung parenchyma with structures of “chunk” sizes less than 0.05 cm, and Models all larger chunks (branches of the bronchial and vessel trees, up to ∼1.5 cm) as randomly‐positioned 2‐D cylinders. The MC code PENELOPE was employed to calculate dose distributions in a water phantom containing a Lung region, Modeled by either a homogenized Lung (as used in conventional planning) or the random Lung Model. Dose calculations used 6 and 18 MV photon beams with four different field sizes.Results: Depth dose curves in the random Lung Model illustrate significant perturbations when the structure size is comparable to the field size. For the 1×1 cm field size, large differences (up to 34% of Dmax) exist in the largest structures due to the loss of CPE with small field size. For large field sizes (10×10 cm or higher), little difference is observed between the random and the homogeneous Models. The additional attenuation of the large structures also results in a region of dose reduction behind the Lung.Conclusion: A new random Lung Model reveals significant dose perturbations from the homogeneous Model, and shows that the homogeneous Model breaks down when the field size is comparable to the structure size. This work is of importance in IMRT planning, where beamlets are used, or in the treatment of small tumors, where small field sizes are used in the planning. This work suggests that in such cases, a more precise description of the Lung geometry, e.g. a high resolution CT‐based pixel‐by‐pixel density map, may be necessary for accurate dosimetry.
